The principle of particles causing a change in electric impedance as they occlude a portion of an aperture between electrically charged vessels is disclosed in U.S. Pat. No. 2,656,508 to W. H, Coulter. Since publication of his patent, considerable effort has been devoted to developing and refining sensing devices operating under the Coulter principle. Relevant United States patents include U.S. Pat. No. 5,376,878 to Fisher; U.S. Pat. No. 6,703,819 to Gascoyne et al.; U.S. Pat. No. 6,437,551 to Krulevitch et al.; U.S. Pat. No. 6,426,615 to Mehta; U.S. Pat. No. 6,169,394 to Frazier et al.; U.S. Pat. No. 6,454,945 and U.S. Pat. No. 6,488,896 to Weigl et al.; U.S. Pat. No. 6,656,431 to Holl et al.; U.S. Pat. No. 6,794,877 to Blomberg et al.; and U.S. Pat. No. 7,417,418 to Ayliffe. All of the above-referenced documents are hereby incorporated by reference, as though set forth herein in their entireties, for their disclosures of technology and various sensor arrangements.
The ability of certain particles to emit radiation at a different frequency than an applied excitation frequency is commonly known as Stokes-shift. Recent United States patents disclosing structure related to interrogation of such phenomena include: U.S. Pat. No. 7,450,238 to Heintzmann, et al.; U.S. Pat. No. 7,444,053 to Schmidt, et al.; U.S. Pat. No. 7,420,674 to Gerstner, et al.; U.S. Pat. No. 7,416,700 to Buechler, et al.; U.S. Pat. No. 7,312,867 to Klapproth, et al.; U.S. Pat. No. 7,300,800 to Bell, et al.; U.S. Pat. No. 7,221,455 to Chediak, et al.; and U.S. Pat. No. 7,515,268 to Ayliffe, et al. All of the above-referenced documents are hereby incorporated by reference, as though set forth herein in their entireties, for their disclosures of relevant technology and various sensor arrangements.